The primary objectives of this study are to examine the rate and extent of recovery following ambulatory orthopaedic surgery and to identify a set of factors that best predict successful surgical recovery. These objectives will be met via a primary surgical outcomes study, investigating clinical and psychosocial influences on recovery of 200 patients undergoing anterior cruciate ligament (ACL) and meniscal surgeries. Patients undergoing ACL surgery will also be recruited into a neuroendocrine and immunology sub-study to assess biological mechanisms of recovery. Recovery is operationalized to include biomechanical and functional parameters, and return to work and sports. The study uses a longitudinal design, a low risk sports medicine clinical sample (e.g., ASA Class I, physically fit, no co-morbid conditions), and a broad measurement framework to identify determinants of musculoskeletal health two years after surgery for ACL and meniscal tears. This is a prospective study: assessment begin prior to surgery and continue at nine standard time intervals up to two years post-surgery. The proposed studies reflect the priorities of the National Institutes of Arthritis, Musculoskeletal, and Skin Disorders by improving understanding of the natural healing process following surgery, by focusing on common sports injuries, and by using a multi-disciplinary framework including both basic and clinical science. By examining the mechanisms associated with rapid and complete postoperative recovery, the results from this research will identify crucial factors that promote recovery after knee surgery. More rapid and complete healing can result in reduced hospital stay, more effective rehabilitation services, quicker return to work and fitness activities, and less risk of re-injury-ultimately reducing both the financial as well as the human costs associated with injury and illness.